Extract Audio from WMV to VOC — Free Online Tool
Extract audio from WMV video files and save it as a VOC file — the classic Creative Labs format used by Sound Blaster cards and DOS-era games. This tool decodes WMV's wmav2 audio stream and re-encodes it to raw unsigned 8-bit PCM (pcm_u8), the native VOC codec, entirely in your browser.
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FFmpeg Command
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Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
WMV files store audio using Microsoft's WMA codecs (typically wmav2), wrapped in the Advanced Systems Format (ASF) container. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed wmav2 audio to raw PCM samples. Those samples are then re-encoded as unsigned 8-bit PCM (pcm_u8) — the default and most compatible codec for the VOC format — and written into a VOC container with the appropriate Creative Labs header structure. Because wmav2 is a lossy codec and pcm_u8 is lossless but lower-resolution than CD audio (8-bit vs. 16-bit), this is a transcoding operation: the audio is fully decoded and re-encoded, not simply remuxed. The output is a raw, uncompressed VOC file suitable for retro applications.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In this browser tool, FFmpeg runs as a WebAssembly module (FFmpeg.wasm) with no server involvement — the same command works identically on a local desktop FFmpeg installation for files over 1GB. |
-i input.wmv
|
Specifies the input WMV file. FFmpeg will parse its ASF container, detecting the video stream (typically msmpeg4) and audio stream (typically wmav2) inside. |
-vn
|
Disables video output entirely, discarding the msmpeg4 video stream from the WMV. Since VOC is a pure audio format with no video support, this flag is required to produce a valid output. |
-c:a pcm_u8
|
Transcodes the decoded wmav2 audio to unsigned 8-bit PCM — the default and most widely compatible audio codec for the VOC format, matching the native output of early Creative Labs Sound Blaster hardware. |
output.voc
|
Sets the output filename and triggers FFmpeg to use the VOC muxer, which writes the Creative Labs VOC header and audio data blocks required for compatibility with DOS applications, Sound Blaster emulators, and DOSBox. |
Common Use Cases
- Extracting dialogue or sound effects from a WMV cutscene to import into a DOS game or a DOSBox-compatible game engine that reads VOC files natively
- Converting Windows Media training or tutorial videos into VOC audio clips for playback on vintage Sound Blaster hardware or emulators
- Archiving WMV-embedded audio into a historically accurate VOC format for retro computing preservation projects
- Ripping ambient music or sound effects from WMV-based multimedia CD-ROMs from the 1990s to reuse in period-accurate demo scene projects
- Preparing audio samples from WMV recordings for use in trackers or MOD music tools that accept raw VOC samples
- Generating VOC audio files from WMV lecture recordings for playback in legacy embedded systems or kiosk hardware that only supports Creative Labs audio formats
Frequently Asked Questions
Yes, in two ways. First, the WMV file's wmav2 audio is already lossy, so some quality was lost when the WMV was originally created. Second, the default VOC codec used here is pcm_u8 — unsigned 8-bit PCM — which has a dynamic range of only 48 dB, noticeably lower than 16-bit audio. The result will sound similar to early Sound Blaster 8-bit playback: clean but with audible quantization noise compared to the original. If your target application supports pcm_s16le, you can modify the FFmpeg command to use that codec for better fidelity.
The VOC format was developed by Creative Labs in the early 1990s, and its default and most universally supported codec is pcm_u8 (unsigned 8-bit PCM). While VOC does support pcm_s16le (signed 16-bit PCM), not all retro software, DOS games, or legacy hardware that reads VOC files can handle the 16-bit variant. The default pcm_u8 ensures maximum compatibility with authentic Sound Blaster environments. If you know your target system supports 16-bit VOC, you can change `-c:a pcm_u8` to `-c:a pcm_s16le` in the FFmpeg command.
Yes. WMV (ASF container) supports multiple audio tracks, and FFmpeg can select a specific one. Add `-map 0:a:1` before the output filename to select the second audio track (index 1), or `-map 0:a:0` for the first. For example: `ffmpeg -i input.wmv -vn -map 0:a:1 -c:a pcm_u8 output.voc`. Without a `-map` flag, FFmpeg defaults to the first audio stream it finds.
No. The VOC format has no metadata support — it was designed as a minimal raw audio container for Sound Blaster hardware and carries only a format header with sample rate and codec information. Any metadata stored in the WMV's ASF container (title, author, copyright, etc.) will be silently dropped during conversion. If metadata preservation matters, consider a format like FLAC or WAV instead.
You can add the `-ar` flag to resample the audio. For example, to output at the classic Sound Blaster sample rate of 22050 Hz, use: `ffmpeg -i input.wmv -vn -c:a pcm_u8 -ar 22050 output.voc`. Common retro-compatible rates are 8000 Hz, 11025 Hz, 22050 Hz, and 44100 Hz. Keep in mind that lower sample rates reduce file size and high-frequency fidelity, which may actually be desirable for period-accurate DOS game audio.
Yes, on the command line you can use a shell loop. On Linux or macOS: `for f in *.wmv; do ffmpeg -i "$f" -vn -c:a pcm_u8 "${f%.wmv}.voc"; done`. On Windows Command Prompt: `for %f in (*.wmv) do ffmpeg -i "%f" -vn -c:a pcm_u8 "%~nf.voc"`. The browser-based tool processes one file at a time, but the displayed FFmpeg command is designed to be copy-pasted for exactly this kind of local batch use.
Technical Notes
The WMV container (technically ASF — Advanced Systems Format) uses Microsoft's wmav2 codec by default, a proprietary lossy codec in the same family as WMA. FFmpeg has a mature open-source decoder for wmav2, so decoding is reliable, but the codec's psychoacoustic compression means the decoded PCM is already an approximation of the original audio. The output VOC format uses Creative Labs' header structure with a block-based layout; FFmpeg writes these blocks correctly for pcm_u8 and pcm_s16le. One important limitation: the VOC format does not support more than one audio channel in the original Sound Blaster spec — stereo VOC files exist but are handled inconsistently by legacy software. If your WMV has stereo audio and you're targeting authentic DOS playback, consider adding `-ac 1` to the command to downmix to mono. Additionally, WMV files with DRM (Digital Rights Management) protection cannot be processed by FFmpeg or this tool — the file must be an unprotected WMV. The absence of audio quality parameters in the VOC format (no `-b:a` bitrate control) is by design: raw PCM has no compression, so quality is determined entirely by bit depth (`-c:a`) and sample rate (`-ar`).